1. Field
Exemplary embodiments of the present invention relate to a device used in an integrated circuit, and more particularly, to a magnetic tunnel junction device.
2. Description of the Related Art
A dynamic random access memory (DRAM) is an exemplary memory device which has been widely used. A DRAM has a feature of operating at a high speed and may be highly integrated. Here, a DRAM is a volatile memory loses data when power is interrupted, and a refresh operation is to be performed to rewrite data periodically.
Also, a flash memory characterized by non-volatility and high degree of integration may have a relatively low operating speed. A magnetoresistive memory device which stores data using a magneto-resistance change may be fabricated as a highly integrated circuit while having non-volatility and high speed operation characteristics.
The magnetoresistive memory device refers to a nonvolatile memory device which stores data using a magneto-resistance changes due to changes in magnetization directions of ferromagnetic materials. The magnetoresistive memory device may include a magneto-resistance element of two magnetic layers. The magneto-resistance element generally has a small resistance when spin directions (magnetic momentum directions) of two magnetic layers are equal to each other and has large resistance when spin directions of the two magnetic layers are opposite to each other. Data may be written to a magnetoresistive memory device by using the fact that the resistance of the magneto-resistance element changes depending on the magnetization states of the magnetic layers.
A magnetoresistive memory device of an MTJ (Magnetic Tunnel Junction) device has a structure of ferromagnetic layer/insulation layer/ferromagnetic layer. When electrons having passed through a first ferromagnetic layer pass through an insulation layer served as a tunneling barrier, a tunneling probability changes depending on a magnetization direction of a second ferromagnetic layer. The tunneling probability becomes a maximum value when the magnetization directions of the two ferromagnetic layers are parallel to each other and the tunneling probability becomes a minimum when the magnetization directions of the two ferromagnetic layers are anti-parallel to each other. The amount of the tunneling current flowing between two ferromagnetic layers depends on the tunneling probability. For example, it may be considered that data ‘1’ (or ‘0’) is written when the tunneling current is large and data ‘0’ (or ‘1’) is written when the tunneling current is small. One of the two ferromagnetic layers serves as a fixed magnetic layer whose magnetization direction is fixed, and the other serves as a free magnetic layer whose magnetization direction is changed in response to an external magnetic field or electric current.
Here, it is difficult to pattern materials constituting an MTJ element, in a general process for manufacturing a semiconductor. A hard mask pattern is generally used for patterning the materials constituting the MTJ element. Since electrode layers disposed over and under an MTJ element are to be patterned by a different patterning process from that of the MTJ element, it becomes more difficult to fabricate a semiconductor device including an MTJ element. A spacer layer may be further formed to protect the MTJ element before patterning the electrode layers. Therefore, a manufacturing process of the semiconductor device may be more complicated.